1. Field of the Invention
The present invention relates to a process for producing an olefin polymer.
2. Description of the Prior Art
It is well known that olefin polymers are produced generally by using a so-called ziegler-Natta catalyst comprising a transition metal compound of groups IV to VI and either a metal or an organometallic compound of groups I to III. In particular, titanium trichloride compositions are used for industrial productions of polyolefins such as polypropylene, polybutene-1, etc. In such a production process, however, an amorphous polymer is produced incidentally to a highly stereoregular olefin polymer of great value for industrial utilization.
This amorphous polymer is of little value for industrial utilization and has much detrimental effect on mechanical properties of the films, fibers, and other processed articles resulting from the olefin polymer, when contained therein in considerable amounts.
The formation of the amorphous polymer means a loss of the feed monomer and requires an additional production facility in order to remove the amorphous polymer, thus bringing about very significant disadvantages also in the industrial aspect.
Consequently, when such an amorphous polymer is not formed at all or is little if any, it will be of very great advantage.
On the other hand, the olefin polymer produced in the above polymerization process contains catalyst residue, which causes problems in the stability, processability, etc. of the olefin polymer. Therefore, facilities are necessary in order to remove the catalyst residue and stabilize the polymer.
This drawback will be removed by increasing the catalyst activity represented by the weight of the olefin polymer produced per unit weight of the catalyst. If the catalyst activity is increased to a great extent, the facility for removing the catalyst residue will be unnecessary and the reduction of the polymer production cost will be possible as well.
Methods for producing titanium trichloride include processes comprising the reduction of titanium tetrachloride (1) with hydrogen, followed by grinding the reduction product in a ball mill to activate it, (2) with metallic aluminum, followed by the same activation as above, and (3) with an organoaluminum compound at a temperature of -30.degree. to +30.degree., followed by the heat treatment of the reduction product at a temperature of 120.degree. to 180.degree. C. These processes, however, are unsatisfactory in both the catalytic activity and the stereo-specificity of the product titanium trichloride.
Further, the following processes have been proposed for producing titanium trichloride: A process comprising treating the solid resulting from the reduction of titanium tetrachloride with an organoaluminum compound, with a complexing agent, followed by reacting the resultant solid with titanium tetrachloride (Japanese Patent Publication No. 3356/78). A process comprising treating the above-mentioned solid reduction product with a complexing agent and titanium tetrachloride (Japanese Patent Publication No. 3480/79). A process comprising reducing an alkoxy group-containing titanium compound with an organoaluminum compound in the presence of an ether compound, and adding titanium tetrachloride and an ether compound to the reaction mixture to form a liquid state titanium compound, followed by heating the compound to reprecipitate a titanium compound (Japanese Patent Application Kokai (Laid-Open) Nos. 18608/81 and 20002/81).
The present inventors, as a result of intensive studies of hydrocarbyloxy group-containing titanium compounds, found that a catalyst system composed of an organo aluminum compound and the following solid catalyst component exhibits a high catalytic activity and gives a highly stereospecific olefin polymer (Japanese Patent Application Kokai (Laid-open) No. 126,402/84). That is, the solid catalyst component containing hydrocarbyloxy groups is prepared by reducing a titanium compound represented by the general formula Ti(OR.sup.1).sub.n X.sub.4-n with an organoaluminum compound, followed by treating the resultant solid with an ether compound and titanium tetrachloride.
According to this method, however, particles of the solid reduction product of the titanium compound represented by the formula Ti(OR.sup.1).sub.n X.sub.4-n disintegrate partially into fine particles during the activation treatment with an ether compound and titanium tetrachloride. In the methods disclosed in Japanese Patent Application Kokai (Laid-Open) Nos. 18608/81 and 20002/81, considerable amounts of fine particles are formed in the solid catalysts since a liquid state titanium compound is once prepared. Accordingly, blocks are formed during the drying of the solid catalyst after washing. When the block-containing solid catalyst is used as such for olefin polymerization, clogging is liable to occur in the solid catalyst feed line and particles of the polymer in the polymerization reactor tend to aggregate into blocks, which may clog the polymer discharge valve. Therefore, the screening of the solid catalyst is necessary in order to remove the blocks.